The invention relates in general to munitions and in particular to electromagnetic guns.
U.S. Pat. No. 4,884,489 issued on Dec. 5, 1989 and U.S. Pat. No. 5,856,630 issued on Jan. 5, 1999 disclose electromagnetic (EM) guns and are incorporated by reference herein. The launcher (barrel) of an EM gun typically comprises a pair of rails separated by a pair of insulators. The interior surfaces of the rails and the insulators form a bore for an armature. During firing of an EM gun, the rails are stressed in a direction away from the bore, while the insulators are usually not stressed. Minimizing rail deflection is an inherent problem in EM guns given that only the rails and not the insulators are loaded during firing. This uneven loading results in the EM launcher cross-section deforming into an elongated oval shape.
Traditionally, EM launchers have relied on prestress to minimize rail deflection. Some methods of obtaining this prestress have included clamped steel laminates, pressure cured epoxy laminates, hydraulically prestressed composites and bolted prestressed steel laminates. In a prestressed design, the load on the rails pushes against the applied prestress in addition to pushing against the stiffness of the materials, therefore lessening the deflection of the rails.
The methods for achieving the prestress are not easy to implement. The methods often result in very heavy guns suitable only for laboratory use. Additionally, for guns not confined to a laboratory setting, insulators with good compression strength are required to achieve the desired prestress levels. This normally resulted in large insulators and an overall oval design for the launcher. The oval design, by itself, results in extra rail deflection because as the jacket is loaded it flattens itself out by compressing the insulators towards the bore.